Commit 761876c8 authored by Jason Wang's avatar Jason Wang Committed by David S. Miller
Browse files

tap: XDP support 



This patch tries to implement XDP for tun. The implementation was
split into two parts:

- fast path: small and no gso packet. We try to do XDP at page level
  before build_skb(). For XDP_TX, since creating/destroying queues
  were completely under control of userspace, it was implemented
  through generic XDP helper after skb has been built. This could be
  optimized in the future.
- slow path: big or gso packet. We try to do it after skb was created
  through generic XDP helpers.

Test were done through pktgen with small packets.

xdp1 test shows ~41.1% improvement:

Before: ~1.7Mpps
After:  ~2.3Mpps

xdp_redirect to ixgbe shows ~60% improvement:

Before: ~0.8Mpps
After:  ~1.38Mpps

Suggested-by: default avatarMichael S. Tsirkin <mst@redhat.com>
Signed-off-by: default avatarJason Wang <jasowang@redhat.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 7c497478

drivers/net/tun.c

+142 −7
Original line number Diff line number Diff line
@@ -73,6 +73,8 @@ 
#include <linux/seq_file.h>

#include <linux/uio.h>

#include <linux/skb_array.h>

#include <linux/bpf.h>

#include <linux/bpf_trace.h>



#include <linux/uaccess.h>
@@ -105,7 +107,8 @@ do { \ 
} while (0)

#endif



#define TUN_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD)

#define TUN_HEADROOM 256

#define TUN_RX_PAD (NET_IP_ALIGN + NET_SKB_PAD + TUN_HEADROOM)



/* TUN device flags */
@@ -224,6 +227,7 @@ struct tun_struct { 
	u32 flow_count;

	u32 rx_batched;

	struct tun_pcpu_stats __percpu *pcpu_stats;

	struct bpf_prog __rcu *xdp_prog;

};



#ifdef CONFIG_TUN_VNET_CROSS_LE
@@ -590,6 +594,7 @@ static void tun_detach(struct tun_file *tfile, bool clean) 
static void tun_detach_all(struct net_device *dev)

{

	struct tun_struct *tun = netdev_priv(dev);

	struct bpf_prog *xdp_prog = rtnl_dereference(tun->xdp_prog);

	struct tun_file *tfile, *tmp;

	int i, n = tun->numqueues;
@@ -622,6 +627,9 @@ static void tun_detach_all(struct net_device *dev) 
	}

	BUG_ON(tun->numdisabled != 0);



	if (xdp_prog)

		bpf_prog_put(xdp_prog);



	if (tun->flags & IFF_PERSIST)

		module_put(THIS_MODULE);

}
@@ -1008,6 +1016,46 @@ tun_net_get_stats64(struct net_device *dev, struct rtnl_link_stats64 *stats) 
	stats->tx_dropped = tx_dropped;

}



static int tun_xdp_set(struct net_device *dev, struct bpf_prog *prog,

		       struct netlink_ext_ack *extack)

{

	struct tun_struct *tun = netdev_priv(dev);

	struct bpf_prog *old_prog;



	old_prog = rtnl_dereference(tun->xdp_prog);

	rcu_assign_pointer(tun->xdp_prog, prog);

	if (old_prog)

		bpf_prog_put(old_prog);



	return 0;

}



static u32 tun_xdp_query(struct net_device *dev)

{

	struct tun_struct *tun = netdev_priv(dev);

	const struct bpf_prog *xdp_prog;



	xdp_prog = rtnl_dereference(tun->xdp_prog);

	if (xdp_prog)

		return xdp_prog->aux->id;



	return 0;

}



static int tun_xdp(struct net_device *dev, struct netdev_xdp *xdp)

{

	switch (xdp->command) {

	case XDP_SETUP_PROG:

		return tun_xdp_set(dev, xdp->prog, xdp->extack);

	case XDP_QUERY_PROG:

		xdp->prog_id = tun_xdp_query(dev);

		xdp->prog_attached = !!xdp->prog_id;

		return 0;

	default:

		return -EINVAL;

	}

}



static const struct net_device_ops tun_netdev_ops = {

	.ndo_uninit		= tun_net_uninit,

	.ndo_open		= tun_net_open,
@@ -1038,6 +1086,7 @@ static const struct net_device_ops tap_netdev_ops = { 
	.ndo_features_check	= passthru_features_check,

	.ndo_set_rx_headroom	= tun_set_headroom,

	.ndo_get_stats64	= tun_net_get_stats64,

	.ndo_xdp		= tun_xdp,

};



static void tun_flow_init(struct tun_struct *tun)
@@ -1217,16 +1266,22 @@ static bool tun_can_build_skb(struct tun_struct *tun, struct tun_file *tfile, 
	return true;

}



static struct sk_buff *tun_build_skb(struct tun_file *tfile,

static struct sk_buff *tun_build_skb(struct tun_struct *tun,

				     struct tun_file *tfile,

				     struct iov_iter *from,

				     int len)

				     struct virtio_net_hdr *hdr,

				     int len, int *generic_xdp)

{

	struct page_frag *alloc_frag = &tfile->alloc_frag;

	struct sk_buff *skb;

	struct bpf_prog *xdp_prog;

	int buflen = SKB_DATA_ALIGN(len + TUN_RX_PAD) +

		     SKB_DATA_ALIGN(sizeof(struct skb_shared_info));

	unsigned int delta = 0;

	char *buf;

	size_t copied;

	bool xdp_xmit = false;

	int err;



	if (unlikely(!skb_page_frag_refill(buflen, alloc_frag, GFP_KERNEL)))

		return ERR_PTR(-ENOMEM);
@@ -1238,16 +1293,77 @@ static struct sk_buff *tun_build_skb(struct tun_file *tfile, 
	if (copied != len)

		return ERR_PTR(-EFAULT);



	if (hdr->gso_type)

		*generic_xdp = 1;

	else

		*generic_xdp = 0;



	rcu_read_lock();

	xdp_prog = rcu_dereference(tun->xdp_prog);

	if (xdp_prog && !*generic_xdp) {

		struct xdp_buff xdp;

		void *orig_data;

		u32 act;



		xdp.data_hard_start = buf;

		xdp.data = buf + TUN_RX_PAD;

		xdp.data_end = xdp.data + len;

		orig_data = xdp.data;

		act = bpf_prog_run_xdp(xdp_prog, &xdp);



		switch (act) {

		case XDP_REDIRECT:

			get_page(alloc_frag->page);

			alloc_frag->offset += buflen;

			err = xdp_do_redirect(tun->dev, &xdp, xdp_prog);

			if (err)

				goto err_redirect;

			return NULL;

		case XDP_TX:

			xdp_xmit = true;

			/* fall through */

		case XDP_PASS:

			delta = orig_data - xdp.data;

			break;

		default:

			bpf_warn_invalid_xdp_action(act);

			/* fall through */

		case XDP_ABORTED:

			trace_xdp_exception(tun->dev, xdp_prog, act);

			/* fall through */

		case XDP_DROP:

			goto err_xdp;

		}

	}



	skb = build_skb(buf, buflen);

	if (!skb)

	if (!skb) {

		rcu_read_unlock();

		return ERR_PTR(-ENOMEM);

	}



	skb_reserve(skb, TUN_RX_PAD);

	skb_put(skb, len);

	skb_reserve(skb, TUN_RX_PAD - delta);

	skb_put(skb, len + delta);

	get_page(alloc_frag->page);

	alloc_frag->offset += buflen;



	if (xdp_xmit) {

		skb->dev = tun->dev;

		generic_xdp_tx(skb, xdp_prog);

		rcu_read_lock();

		return NULL;

	}



	rcu_read_unlock();



	return skb;



err_redirect:

	put_page(alloc_frag->page);

err_xdp:

	rcu_read_unlock();

	this_cpu_inc(tun->pcpu_stats->rx_dropped);

	return NULL;

}



/* Get packet from user space buffer */
@@ -1266,6 +1382,7 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 
	bool zerocopy = false;

	int err;

	u32 rxhash;

	int generic_xdp = 1;



	if (!(tun->dev->flags & IFF_UP))

		return -EIO;
@@ -1324,11 +1441,13 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 
	}



	if (tun_can_build_skb(tun, tfile, len, noblock, zerocopy)) {

		skb = tun_build_skb(tfile, from, len);

		skb = tun_build_skb(tun, tfile, from, &gso, len, &generic_xdp);

		if (IS_ERR(skb)) {

			this_cpu_inc(tun->pcpu_stats->rx_dropped);

			return PTR_ERR(skb);

		}

		if (!skb)

			return total_len;

	} else {

		if (!zerocopy) {

			copylen = len;
@@ -1402,6 +1521,22 @@ static ssize_t tun_get_user(struct tun_struct *tun, struct tun_file *tfile, 
	skb_reset_network_header(skb);

	skb_probe_transport_header(skb, 0);



	if (generic_xdp) {

		struct bpf_prog *xdp_prog;

		int ret;



		rcu_read_lock();

		xdp_prog = rcu_dereference(tun->xdp_prog);

		if (xdp_prog) {

			ret = do_xdp_generic(xdp_prog, skb);

			if (ret != XDP_PASS) {

				rcu_read_unlock();

				return total_len;

			}

		}

		rcu_read_unlock();

	}



	rxhash = __skb_get_hash_symmetric(skb);

#ifndef CONFIG_4KSTACKS

	tun_rx_batched(tun, tfile, skb, more);

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